Improving the Density of Functional Fabrics to Protect Radiation Workers in Radiology Departments

Abstract

In medical institutions, the high weight of shielding clothing restrains the activities of medical workers. Although lightweight shielding clothing is being manufactured to solve this problem, the weight can only be reduced by 10%–20%. Flexible shielding fibers are mainly used to minimize activity restrictions; however, it is difficult to maintain the reproducibility of shielding performance. When weaving fibers with a yarn that contains a shielding material, the content of the shielding material in the yarn, tensile strength, and problems encountered during weaving should be considered. Therefore, in this study, a high-density shielding fabric weaving process was developed to weave a functional shielding fabric for actively utilizing it for low-dose shielding. The yarn was manufactured using 5 wt% barium sulfate, and the shielding performance was evaluated using the existing plain weave and two fabrics that underwent the newly developed high-density twill weave process. As a result of the experiment, the density of the fabric woven by the twill method increased by 82 g/m³, documenting a difference of 7.46% in the high-energy region and 11.71% in the low-energy region, thus indicating that the Twill method improves the shielding effect. Therefore, it is possible to mass produce lightweight, high-density shielding fabric that can protect against scattered rays that represent the main source of radiation in medical institutions.

1. Introduction

The protective clothing for shielding diagnostic X-rays used in medical institutions is developed for radiation workers in medical institutions, and the shielding performance is determined according to the dose and released into various products. Particularly, the values of shielding performance used in the medical field are 0.25 mmPb and 0.50 mmPb based on the lead equivalent [1,2]. Recently, the weight reduction in the radiation shield was required for the ease of activity for medical personnel. However, as the shielding garment manufacturing process technology that maintains the shielding performance for X-rays for medical diagnosis required to meet the light weight condition has technical limitations, lightweight shields are manufactured separately for indirect and direct rays according to the lead equivalents [3]. Accordingly, to develop a new shield suitable for radiation protection in medical institutions, new process technologies and research on shielding composite materials are needed [4,5,6,7].

Generally, radiation shields are manufactured in the form of fibers, sheets, and films, and most of the materials used for shielding clothing in medical institutions are manufactured in the form of a rubber-based sheet mixed with polymer to maintain flexibility. A metal-based thin film is employed for shields necessary for the inner parts of medical devices, such as radiographic barriers or X-ray generators, considering their thickness and strength [8,9]. Although fiber-type materials lack shielding performance compared with sheets or films, they have improved flexibility. They are mainly used in the form of composites in combination with other materials [10].

Two process technologies can be applied to the manufacturing of shielding fibers. The most commonly used process technology is lamination, in which a liquid shielding material mixed with a polymer material is coated onto a nonwoven fabric [11]. However, this process technology has a disadvantage in that it is difficult to maintain the reproducibility of the shielding performance owing to the non-uniform dispersion of the shielding material particles and control of the coating thickness. In addition, when used for a long period, cracks are generated on the surface owing to the hardening phenomenon, which reduces the stability of the product [12]. The second most commonly used process technology involves weaving shielding fiber using manufacturing shielding yarn impregnated with shielding material. However, these process technologies have limitations regarding their capacities to improve the shielding performance owing to the limited amount of shielding material injected and the problem of pinholes occurring in the fabric during weaving [13,14].

Among studies focused on manufacturing shielding fibers, various studies such as a new weaving process technology for manufacturing a shielding fabric using yarn and a technology for laminating multiple layers of fabric have been conducted [15,16]. However, a method to improve the shielding performance while maintaining the flexibility of the fiber may not exist.

Unlike polymer-based shielding sheets or metal-based thin films, shielding fibers have excellent flexibility, are lightweight, and exhibit high-perceived comfort while in direct contact with the skin. In addition, shielding fibers have emerged as a major material in research related to shielding materials due to their wide range of practical applications, including linings for shielding clothing, blankets for radiation protection required for diagnostic tests, and curtains [17,18].

This study intends to weave a lightweight functional shielding fabric that can secure flexibility and exhibit shielding performance against scattered radiation and low-dose radiation of diagnostic X-rays. In addition, the manufacturing of various types of products with the developed functional shielding fabric is proposed.

To address the issues associated with the production of the existing shield, this study integrated a method of weaving the fabric by developing the yarn that is impregnated with the shield material instead of coating the shield material. In this method, it is possible to maintain the reproducibility of the shielding performance when manufacturing the shield. Additionally, a high-density fabric weaving process was developed to prevent the exposure of scattered rays corresponding to indirect ray instead of direct ray shielding, and this concept was aimed at solving the problem of pinholes occurring inside the fabric. The purpose of this study is to develop a new concept for manufacturing lightweight shielding fabrics. Therefore, this study developed a yarn development concept that can improve the content of shielding materials and a weaving process technology that can improve the density of shielding fabrics and compared and evaluated the shielding performance of existing shielding fibers and the developed shielding fibers. It is thought that the shielding fiber produced in this manner can be used as lining for aviation crew underwear, for regular shielding clothes, and for work clothes for workers in nuclear power plants [19,20].

Therefore, the aim of the research is to study the process from the manufacturing stage of shielding yarn to the fabric weaving stage and present the characteristics of the process technology in a step by step manner for the mass production of X-ray shielding fabric in the future. In addition, the study quantitively presents the X-ray protection effect through the evaluation of the shielding performance of the woven shielding fibers. The limitation of the manufacturing of shielding fibers using the existing laminate process technology is mass production, and in the case where the weaving method that includes shielding materials in a yarn is used, the shielding performance may be affected due to the limitation of the shielding material content. Therefore, the core of the process technology developed in this study is to manufacture the yarn by maximally impregnating barium sulfate while maintaining the proper strength of the yarn, and to improve the shielding performance of the finally manufactured shielding fiber by applying the high-density weaving process.

2. Materials and Methods

The most important physical property of a radiation shield is its density [21]. Density is a measure of the mass per unit volume of a material and determines its radiation-shielding capacity [22]. Therefore, the higher the density, the better the shielding performance is. This property helps increase the interaction probability between the radiation incident photon and absorbing material inside the shield [23].

The mean free path of a single-energy photon incident on the shield from the X-ray generator is the average distance (d) that the photon travels when the photon and shielding material atom collide. The mean free path depends on the photon energy and material, as shown in Equation (1) [24]:

$$d={\mu }^{-1}={\left[\left(\frac{\mu }{\rho }\right)\rho \right]}^{-1},$$

(1)

where $\mu$ is the linear attenuation coefficient, $\frac{\mu }{\rho }$ is the mass attenuation coefficient, and $\rho$ is the density of the shield. The attenuation coefficient is proportional to the mass or density as it is proportional to the number of atoms per unit volume of a substance. Therefore, the mass attenuation coefficient can be presented by dividing it by the density ($\rho$). In addition, it can be confirmed that the method of increasing the area and density of the shield considerably improves the shielding performance.

To increase the density of the shielding fibers to be manufactured, this study aimed to improve the shielding performance by increasing the content of the shielding material in the yarn to solve the structural problems that occur during weaving [25]. Therefore, the master batch manufacturing process for yarn production is shown in Figure 1.

Prior to weaving the shielding fabric, yarn with shielding performance was developed. Barium sulfate, an ecofriendly material that is harmless to the human body, was selected as the primary shielding material in the yarn. Pure barium can be harmful when introduced into the body, but barium sulfate is a stable compound, so it does not dissolve in water or stomach acid and has difficulty ionizing; hence, it has little effect on the human body [26,27]. In addition, barium sulfate has a density of 4.5 g/cm³, which is lower than that of tungsten, but is effective for yarn production as it is not soluble in water [28]. First, a master batch was manufactured using a polymer for polyester (PET, Huvis, 2022) fibers, containing barium sulfate. The inorganic molecular weight of the barium sulfate powder used (Sigma–Aldrich, St. Louis, MO, USA, 2022) was 233.39 g/mol, and the mixing conditions were optimized to 50 wt% considering the characteristics of the material and the sizes and shapes of the inorganic particles during the manufacturing of the master batch chip. The manufactured barium-sulfate-based master batch chip is shown in Figure 2. In the master batch chip manufacturing process, the size of the shielding material particles affects the content; in general, the smaller the particle size, the higher the weight percentage.

In addition, PET yarn was manufactured using a master batch based on barium sulfate. The radiation-shielding yarn was manufactured as a multifilament with a density of 75 denier/36 filaments using a melt-spinning process. Before performing the melt spinning process, the spinning temperature, extrusion time, and spinning peck design were designed subject to the conditions listed in

Table 1. Design of melt-spinning process conditions for the development of fiber yarns containing barium sulfate (5 wt%).

Condition	Adjustable Value
Content of fine particles in fiber (wt%)	5
Extruder temperature range (°C)	280–300
Extruder pressure (Pa)	1.2 × 10−4
Spinning pack temperature (°C)	295
Spinning pack pressure (Pa)	1.2 × 10−5
Cooling time (s)	0.52
Take-off roll speed (revolutions per minute (rpm))	3.450

, and the melt-spun yarn was manufactured by spinning, guiding, drawing, and winding [29]. In addition, the conditions were designed to have barium sulfate contents up to 5 wt% during yarn development.

The yarns containing barium sulfate were analyzed using scanning electron microscopy (SEM). The dispersibility of barium sulfate in the shielding yarn was observed via field-emission scanning electron microscopy (FESEM, S-4800, Hitachi, Tokyo, Japan) by sectioning the prepared sample with a microtome (RM2235, Leica). The results of this analysis are shown in Figure 3. A visual analysis of the barium sulfate-containing yarns is provided in Figure 4.

The yarn containing the shielding material must maintain a proper tensile strength while concurrently maintaining the shielding performance so that the fabric can be woven through the weaving machine without damaging the yarn. Considering these conditions, the physical properties of the shielding yarns containing barium sulfate developed in this study are listed in

Table 2. Physical properties of shielding fiber yarn.

Characteristic	Yarn Containing BaSO4
Fineness (Denier)	75.1
Tensile strength (g/d)	3.15
Elongation at break (%)	28.1
Mineral contents (wt%)	5
Twist per meter	75 deniers/36 filaments

.

Two radiation-shielding fiber fabrics were woven using the developed shielding yarn, as shown in Figure 4. The weaving conditions were the same for both fabrics, but the fabric depicted in Figure 5a was woven using the plain-weaving process, and that shown in Figure 5b was woven using the twill-weaving process.

To evaluate the medical radiation shielding performance of the shielding fiber, the geometric conditions were set as shown in Figure 6, and the shielding ratio of the fiber was calculated as (1 − $\frac{W}{W_0}$) × 100 [30,31]. Herein, $W$ is the dose measured when there is a shielding fiber between the X-ray tube and dosimeter, and $W_0$ is the measured exposure dose when there is no shielding fiber between the X-ray tube and dosimeter.

The energy source used in this experiment was an X-ray generator (Toshiba E7239, 150 kV–500 mA, 1999, Tokyo, Japan) used in a medical institution. Although there exists a method of evaluating the shielding performance according to the distance by measuring the space dose, in this study, the shielding rate of the area wherein the direct ray was generated, was evaluated using the average energy of the X-rays used in the diagnostic area [32]. A calibrated DosiMax plus I detector (IBA Dosimetry Corporation, Gewerbegebiet Frauenholz, Schwarzenbruck, Germany) was used with consideration that a distance was left behind the detector to eliminate the contribution of backscatter radiation in our measurements [33].

3. Results

Two types of shielding fibers were produced using the conventional plain-weaving and twill-weaving methods, and the properties of the two fabrics were compared and evaluated to determine the shielding effect of fabric woven with yarn containing barium sulfate. Figure 7 shows the results of the comparison of the woven shielding fibers according to the tissue composition. It was observed that the fabric composed of twill tissue was denser than that composed of plain tissue. It can be confirmed that the twill process requires more yarn, and thus, the fabric has a higher density. As a result, no voids appear.

The density and characteristics of the tissue for the development of shielding functional fabrics for medical radiation are listed in

Table 3. Mechanical properties of plain and twill fabrics.

Weaving Method	Tensile Strength (N)		Elongation at Break (%)		Tearing Strength (N)		Specific Weight (g/m²)	Thickness (mm)	Density (g/m³)
Twill	warp	810	warp	3.13	warp	20.84	165–170	0.23–0.25	232
	weft	460	weft	26.5	weft	17.51			120
Plain	warp	740	warp	34	warp	16	114–118	0.19–0.20	150
	weft	290	weft	20	weft	9			74

Tensile strength and elongation at break were measured according to the Korean Standard K 0520:2015, and tearing strength was measured according to the test method of the International Standardization Organization 13937-2:2000.

. Both the strength and weight are quantitatively higher than those of the twill tissue, and the final fiber thickness is higher in the twill tissue than in the plain tissue. As for the mechanical properties of the woven fabric, the density of the fabric woven with the twill structure was improved by a value of approximately 50%. In addition, this could be ideal for sewing clothes as it shows a large difference in tear strength and tensile strength.

The strength of the developed shielding fabric was compared and evaluated according to the twill and plain weave methods based on the weft and warp yarns. As shown in Figure 8, weaving is more effective in terms of strength if the twill method is used.

The medical radiation-shielding fibers are depicted in Figure 9. The fabric is woven using the conventional, plain method (Figure 9a) and using the high-density twill-weaving method (Figure 9b), which is a high-density weaving method.

Table 4. Comparison of shielding performance of medical radiation shielding fibers.

Radiation Type	X-ray Energy (kVp)	Mean of Exposure (µR)			Shielding Rate (%)
		Nothing	Plain	Twill	Plain	Twill
X-ray	40	121.23	90.91	74.87	24.01	37.24
	60	421.22	337.19	294.22	18.95	29.15
	80	911.84	765.12	666.19	15.09	25.94
	100	1534.62	1313.33	1210.51	13.42	20.12
	120	1829.12	1698.89	1610.72	6.12	10.94

summarizes the shielding performance evaluation results obtained using the medical radiation energy employed for diagnosis. The experimental results are presented based on the shielding performance in the direct ray area. When the experiment was conducted with an X-ray tube voltage of 80 kVp, the plain weave fabric had a shielding rate of 15.09%, but the high-density twill weave fabric had a shielding rate of 25.94%. Differences of 7.46% and 11.71% were noted in the high- and the low-energy regions, respectively, indicating that, typically, the high-density twill-woven fabric has a superior shielding performance than the plain-woven fabric.

4. Discussion

Exposure of medical personnel and patients to medical radiation is affected by the scattered radiation generated in diagnostic X-ray laboratories. Scattered rays are secondary rays generated when the primary direct ray interacts with the inspection target or surrounding materials. These rays typically cause low-radiation doses (≤100 mSv) [34]. In addition, given that even a low dose can have an effect on the human body, active shielding of medical workers is required [35]. However, most of them wear lead shielding suits greater than or equal to 2.8 kg instead of conventional shielding suits that are made to protect against scattering radiation. This might be burdensome on the body. Furthermore, it is desirable to always wear such protective clothing in the operating room or cardiovascular examination room, regardless of the distance from the source [36]. To avoid exposure to X-rays in the medical diagnostic field, medical staff sometimes place themselves sufficiently far from the X-ray source rather than wearing shielding suits, owing to the movement restrictions imposed by the weight of such suits [37].

The high-density shielding fabric developed in this study shows a shielding rate of approximately 20% with respect to the direct ray at the point where the tube voltage of 100 kVp and the dose of 1200 μR is generated. The conversion of this point of occurrence to a distance implies a distance of 1 m or more from the point of radiation. In other words, the developed shielding fabric can be used as a fabric for lightweight functional shielding clothing at a point at a minimum distance of 1 m from the radiation generating device [38]. In addition, for a shielding rate of approximately 20% for direct rays, it is considered that over 50% shielding effect occurs for indirect rays, and this might be attributable to the distance inverse square law and directionality of dose [39]. In areas with low doses of medical radiation, lightweight functional shielding clothing is expected to increase the activity and psychological stability of medical workers [40].

The lightweight functional shielding clothing used for shielding scattered and indirect rays generated in medical institutions are manufactured using a lamination process that involves resin. However, when a user wears such a shielding suit for a long time, it can result in several problems, including lack of ventilation. In this study, a high-density woven fabric was developed using a yarn containing a shielding material. In previous studies, there have been many cases of weaving failure owing to the yarn strength when functional fabrics were weaved for radiation shielding [41]. Furthermore, the lack of technical elements to maintain proper strength has made it difficult to commercialize these fabrics as products. In addition, in a technical study wherein the yarn of the shielding material was deposited over a tungsten wire, there was the disadvantage of poor flexibility when the system was used for a long time owing to the tungsten wire. In addition, it was difficult to match the yarn strength in the process technology. The strength of the yarn developed in this study was 3.15 g/d, which is considered to be advantageous for mass production as this strength is the same as that of the PET yarn used for everyday clothes; accordingly, it can be produced using a general weaving machine. Figure 10 shows the functional shielding underwear for female radiation workers fabricated using the shielding fiber developed in this study. Fabrication of shielding suits for radiation workers––similar to those worn by flight attendants or medical institution workers––can eliminate the discomfort caused by the weight of such suits by using the developed shielding fibers and can help radiation workers achieve psychological stability [42].

To prevent exposure to low-dose radiation, a shield in the form of clothing that can be worn at all times is required. Particularly, for workers operating within a certain distance range, a customized shielding system is required depending on the dose [43]. In previous studies, a liquid mixture of a polymer material and shielding material was coated onto a nonwoven fabric to produce shielding fibers. A mass production technology was proposed in this study by developing a high-density weaving method that can decrease the production time. The results of this study indicate that the proposed method will be effective in protecting against low-dose scattering radiation. One of the limitations of this study is that only barium sulfate was used to manufacture the yarn. In the future, it will be necessary to develop yarns composed of various materials, such as boron and bismuth oxide [44].

In addition, although a method of impregnating barium sulfate in yarn was proposed previously, it has been mostly used for weaving fibers for glossy materials, and the barium sulfate content is 2 wt% at most, making these materials far from being capable of radiation shielding. Therefore, more research is needed in the future to achieve mass production while increasing the content to 5 wt% or more and maintaining the same tensile strength.

5. Conclusions

In this study, an X-ray shielding fabric was developed to shield low-dose areas of medical radiation. To solve the problem of reproducibility of the shielding performance that occurs when the fabrication uses the existing lamination process, the shielding material was directly impregnated into the yarn and woven into the fabric. A future study intends to improve this further through the low-temperature fusion technology that can apply various shielding materials and increase the shielding material content by up to 20 wt% while maintaining the yarn’s tensile strength. The shielding performance of fabrics produced by twill-weaving, which is a high-density weaving method, is improved by an average of 9.5% compared with that of plain woven fabric (produced via conventional weaving). In addition, the twill-tissue method can improve the density of the shielding fabric as a high-density weaving method and can solve the pinhole problem. Therefore, when producing fabric that can be worn at all times for low-dose shielding in medical institutions, the high-density twill-weaving method is advantageous in providing active shielding.